1. Field of the Invention
The invention relates to a method and apparatus for automatically and continuously balancing the opposing thrust forces that are inherently generated in the operation of, for example, a turbine-driven, oil well pump. Such units are commonly supported at the bottom of a well by a tubing string and the thrust forces generated by the pumping portion of the unit in a downward direction generally are significantly larger than the oppositely directed thrust forces generated by the operation of the turbine which drives the pump. The balancing of the excess downward thrust force is very desirable since the thrust capacity of any conventional bearings that could be employed in the unit is severely limited by the diametrical constraints of the oil well casing within which the pump is disposed. Additionally, an unbalanced downward thrust load of any appreciable magnitude would affect the size of the tubing string required for suspending the turbine-driven, pumping unit within the well.
2. Description of the Prior Art
Thrust bearings have heretofore been employed in turbo-driven pumps for oil wells which are of the hydrostatic type. Such bearings essentially comprise a circular flange connected to the pump shaft and have annular chambers disposed on opposite sides of the circular flange and respectively connected to pressure sources. The lips of the annular chambers are disposed in close proximity to the adjacent rotating face of the flange and the effective pressure exerted by each annular chamber on the flange is a function of the axial spacing of the flange relative to such lips. The shaft and flange can move axially to a limited extent. Hence, if the flange is moved with the pump shaft as a result of an unbalance of the thrust forces between the pump and turbine, it will move closer to lips of one annular chamber and farther from the lips of the annular chamber disposed on the opposite side of the annular flange. This results in an increase in effective pressure on the side of the flange moving closer to a chamber, and a decrease in effective pressure of the chamber on the opposite side of the flange from which it is moving away. This action thus results in a pressure force operating on the one side of the flange to return it (and the attached shaft) to its normal position where it is approximately centered between the lips of the annular chambers respectively disposed on its opposite sides.
This prior art system for compensating for thrust imbalance in a fluid driven oil well pump has the disadvantage that whenever the thrust imbalance becomes severe, for example, when the gas content of the fluid being pumped increases suddenly, the gap between the lips of the annular chamber toward which the thrust flange moves as a result of the imbalance becomes so narrow that contact occurs and the thrust bearing is effectively destroyed.
U.S. Pat. No. 3,847,512 discloses the utilization of balancing forces for application to opposite sides of a piston.